Papers by Keyword: Oxyapatite

Abstract: The amount and alignment of hydroxyl ions influence the bioactivity of hydroxyapatite. Hydroxyl ions in hydroxyapatite are the most mobile and upon heating are the first to leave the lattice to form oxyhydroxyapatite. This work describes a method for producing hydroxyapatite with different amounts of hydroxyl ions, and reports on the changes in Fourier transform infrared absorption at increasing level of dehydroxylation. Detailed analysis of spectra in the 500 – 700 cm^-1 range showed a peak shift for the hydroxyl ion absorption line at 632 cm^-1 to 637 cm^-1 and an increase in the wavenumber for the phosphate line at 575 cm^-1.

Abstract: Tetracalcium phosphate (TTCP) requires the highest synthesis temperatures of all the calcium phosphates, but now a new process is available at 400 °C lower than previously, at 900 °C. Instead of ball-milling reactants for a homogeneous mix, the reactants were included in an amorphous phase. Heating produced hydroxyapatite, oxyapatite and then TTCP. Amorphous nanoparticles were synthesized and heated in air or in vacuum. The sequence of solid-state reactions were tracked with X-ray diffraction and Fourier transform infra-red spectroscopy. Heating in air stabilized the carbonate containing apatite, thereby requiring higher temperatures for decomposition, as per previous studies. Heating in vacuum promoted oxyapatite; a critical step for reaction with calcium oxide to generate TTCP. This faster process enables production at a lower temperature and reduces the use of ball milling for producing fine TTCP powders.

Abstract: Calcium phosphate coating films were fabricated on Ti-6Al-4V plates and screw-type implants with a blast-treated surface using radiofrequency (RF) magnetron sputtering and were evaluated in vitro and in vivo. Amorphous calcium phosphate (ACP) and oxyapatite (OAp) films obtained in this study could cover the blast-treated substrate very efficiently, maintaining the surface roughness. For the in vitro evaluations of the calcium phosphate coating films, bonding strength and alkaline phosphatase (ALP) activity were examined. The bonding strength of the coating films to a blast-treated substrate exceeded 60 MPa, independent of film phases except for the film after post-heat-treatment in silica ampoule. When compared with an uncoated substrate, the increase in the ALP activity of osteoblastic SaOS-2 cells on a calcium phosphate coated substrate was confirmed by a cell culture test. The removal torque of screw-type Ti-6Al-4V implants with a blast-treated surface from the femur of Japanese white rabbit increased with the duration of implantation and it was statistically improved by coating an ACP film 2 weeks after implantation. The in vitro and in vivo studies suggested that the application of the sputtered ACP film as a coating on titanium implants was effective in improving their biocompatibility with bones.

Abstract: Impedance spectroscopy was used to measure the changes of electrical properties during the isothermal crystallisation of the phosphate phase in bulk samples of a glass with nominal molar composition (3CaO.P2O5)20(SiO2)35(MgO)38.354(K2O)6.646, developed for biomedical applications. Crystallization studies were performed in isothermal conditions at 800°C and 860°C, and were monitored by impedance spectroscopy. XRD shows that a stable orthophosphate phase, Ca9MgK(PO4)7 crystallizes at about 860°C, after formation of earlier phosphate precursors formed at lower temperatures, namely oxyapatite (Ca5(PO4)3O) and tricalcium phosphate (Ca3(PO4)2). The conductivity of bulk glass samples decreases at 800°C, as the phosphate precursors phases crystallize. The opposite trend is observed on crystallizing the orthophosphate phase, at 860°C.